Study On Differences Of Extracellular Enzyme Activity And Microbial Community In Rhizosphere Soil At Different Elevations Of Broad-leaved Forest In Qinling Taibai Mountain

The rhizosphere is the gateway for nutrients,moisture and other substances to enter the plant root system.Rhizosphere microbes are an important part of the micro-ecosystem of plant roots,and play an important role in the decomposition of soil organic matter,the absorption of various nutrients and the growth of vegetation.Microbes in the rhizosphere soil are jointly affected by various factors such as soil,vegetation,climate,etc.Although there are many studies on rhizosphere microbes,the results are not consistent.Qinling Mountain is the boundary line between north and south in China.It has rich and special animal and plant diversity characteristics.Its main peak,Taibai Mountain,is the highest peak in Qinling Mountains.The huge elevation difference and the special geographical environment conditions of Taibai Mountain make the vertical belt spectrum of mountain soil,vegetation and climate complex and distinct,so it provides a natural experimental platform for us to study the characteristics of rhizosphere soil extracellular enzyme activity and microbial community.In this study,the rhizosphere soils of four typical vegetation types with ten elevation gradients of 1300 m to 2600 m above the northern slope of Taibai Mountain in Qinling Mountain were taken as the research objects,research the elevation distribution pattern of soil physicochemical properties,extracellular enzyme activity and microbial community in the rhizosphere of Taibai Mountain,and analysis of the interaction between soil-microbe-plant communities in the rhizosphere soil.The main research progress and conclusions are as follows:(1)In the middle and low elevations of 1300 m ~ 2600 m of Taibai Mountain,it has high species diversity and richness.With the increase of elevation,the typical vegetation types in the area from the bottom to the top are Quercus aliena var.acutiserrata forest,Quercus liaotungensis forest,Betula albo-sinensis forest and Betulaalbo-sinensisvar.sepentrionalis forest.The species diversity(Shannon diversity)and richness index of trees,herbs and shrubs are all higher in the Quercus liaotungensis forest and Betula albo-sinensis forest,that is,the elevation is 1915 m ~ 2405 m.(2)With the increase of elevation,the physicochemical properties and microbial biomass indicators of rhizosphere soil showed significant changes with different trends.In different vegetation zones,there were no significant differences in rhizosphere soil p H,soluble organic nitrogen,C: N ratio,MBP,MBC: MBN ratio and MBN: TN ratio.It shows that the influence of elevation on the rhizosphere soil physicochemical properties and microbial biomass is greater than that of vegetation zone.Rhizosphere soil properties such as p H,water content,bulk density,soluble organic carbon,and ammonium nitrogen mainly had a significant relationship with the characteristics of shrub communities,while rhizosphere soil C,N,P and their ecological stoichiometric ratios and microbial biomass C,N,P and their ecological stoichiometric ratios were mainly significantly related to the characteristics of trees and herbs communities.(3)With the increase of elevation,the activities of extracellular enzymes BG,BX,CBH,NAG,and AKP in the rhizosphere soil showed a trend of increasing first and then decreasing,and the enzyme activities were highest at an elevation of 1915 m;BG: NAG,BG: AKP and vector length are larger at low elevation,NAG: AKP ratio increases first and then decreases with increasing elevation,and vector angle is higher at high elevation,indicating that the rhizosphere soil has a relatively strong C limit at low elevations and a relatively strong P limit at high elevations.In different vegetation zones,the five extracellular enzyme activity in the rhizosphere soil was significantly higher in the Quercus liaotungensis forest and Betula albosinensis forest zone than the other two vegetation zones,while the ecoenzymatic stoichiometric ratios were significantly greater in the Quercus aliena var.acutiserrata forest zone than the other three vegetation zones.The main influencing factors of extracellular enzyme activity in rhizosphere soil with elevation are plant community diversity,rhizosphere soil moisture content,bulk density,C,N,P,microbial biomass C,N,P,MBC: MBN ratio and MBC: SOC ratio.(4)The overall alpha diversity index of rhizosphere soil microbes is: bacteria > arbuscular mycorrhizal fungi > fungi.Elevation has a very significant effect on the alpha diversity of bacteria,fungi and arbuscular mycorrhizal fungi in the rhizosphere,while the vegetation type has little effect on the alpha diversity of bacteria and fungi.The microbial beta diversity showed obvious separation effect at different elevations and vegetation types.The main dominant phylum of bacteria,fungi and arbuscular mycorrhizal fungi showed significant changes at different elevation gradients with different trends.In contrast,the composition of microbial communities differed slightly between different vegetation zones.The main driving factors of microbial community changes with elevation are plant community diversity,rhizosphere soil C,N,P,water content,and microbial biomass C,N,P.